Observation of change in the oxidation state at ferromagnet/insulator interface upon thermal annealing

It is reported that the magnetoresistance (MR) of magnetic tunneling junction (MTJ) like Co1 - xFex/Al2O3/Co1 - xFex improves upon thermal annealing. We investigate the mechanism of this improvement by comparing the X-ray absorption spectra (XAS) of half-MTJ structures (Co84Fe16/Al2O3) before and after annealing. Before annealing, XAS show the presence of few angstroms of Co-and Fe-oxides, which disappeared after annealing at 250 °C for 1/2 hour. We attribute enhanced MR upon annealing to the disappearance of Co and Fe oxides at the interface which reduce the spin-polarization of the conduction electrons and cause spin-flip scattering, both leading to inferior performance of MTJ.